In the process of injection molding plastics, plasticizers and injection apparatuses are customarily used. Typically, a plasticizer and an injection molding screw plasticize plastic material. The melt is then injected into an injection molding tool by an axial movement of the screw. To prevent the melt from backflowing during the injection process, a non-return valve is usually disposed at the end of the screw.
Recently, the demand for dimensionally small injection-molded parts has increased. Common examples of such parts include micro-mechanical components (e.g., micro gear wheels for watches), medical-technical hardware, and optoelectronic elements (e.g., parts for optical waveguides).
The production of these small part encounters problems when manufactured with classical injection molding machines, however. The problem relates to the small amounts of hot thermoplastic that must be injected into the usually cold mold. This necessarily results in a critical thermal transition region in the end region of the screw or in the nozzle region.
The present invention is directed to avoiding this thermal transition region or minimizing its effect, especially when injection molding small injection molded parts, to achieve precise metering of the quantity of injection-molding material, such as plastic, which is injected. Specifically, the inventive method and an apparatus can produce and deliver even the smallest quantities of melt to yield small and even ultra-small molded parts by precisely controlling the dose. The pressure buildup here preferably occurs as close to the cavity as possible.
In general, according to one aspect, the invention features a method for injecting plastic material or other injectable material into an injection molding tool. The method comprises plasticizing or melting the plastic or other injectable material in a plasticizing, or similar, apparatus. The material is then transported into a dosing. or metering, apparatus, which has a fluidic connection to the plasticizer apparatus. Preferably, the amount of material is essentially precisely the quantity that is to be introduced into the injection molding tool. The material is then transported, essentially in that quantity which is to be introduced into the injection molding tool, from the metering apparatus into an injection apparatus, via a fluidic connection, while at the same time the material is prevented from flowing from the metering apparatus back into the plasticizing apparatus. The entire quantity injectable material, which is situated in the injection apparatus, is injected into the injection molding tool, while at the same time the material is prevented from flowing from the injection apparatus back into the metering apparatus.
Preferably, provision is here made that the injectable material that is situated in the injection apparatus is temperature-stabilized in such a way that it remains a liquid melt.
In general, according to another aspect, the invention also features an apparatus for injecting plastic material or other injectable material into an injection molding tool. The apparatus comprises a plasticizing apparatus, in which plastic material or another injectable material is plasticized. A fluidic connection is provided between the plasticizing apparatus and a metering apparatus. The metering apparatus functions to take-up a prescribed quantity of injectable material. Preferably, an element, such as a non-return valve, is disposed in the connection, to prevent the injectable material from backflowing. A fluidic connection is also provided between the metering apparatus and an injection apparatus. The injection apparatus receives the injectable material that is to be injected into the molding tool before it is injected. The quantity of injectable material that is transported into the injection apparatus essentially corresponds to the quantity that is to be introduced into the injection molding tool, in the preferred embodiment. Finally, means is provided to prevent the injectable material from flowing from the injection apparatus back into the metering apparatus.
In the preferred embodiment, the means that prevents the injectable material from flowing from the injection apparatus back into the metering apparatus is implemented by an injection piston, which blocks the fluidic connection between the metering apparatus and the injection apparatus during the injection process.
Also, preferably, the means to prevent the injectable material from flowing from the injection apparatus back into the metering apparatus is implemented using an injection piston, which blocks the fluidic connection between the metering apparatus and the injection apparatus during the injection process.
Finally, the injection apparatus is ideally surrounded by temperature-stabilizing heaters, for example, at least in part, which prevents solidification of the melt.
In summary, the inventive method and design advantageously achieve a pressure buildup in the melt during the injection process that occurs very close to the cavity. This results in a higher quality injection molding process, since the method and apparatus make it possible to meter and measure exactly the injected plastic, while at the same time reducing or controlling the thermal transition.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.